Eye tracking systems are used in a variety of applications, mostly in the medical field like in connection with systems for surgery or diagnosis. An eye tracking system typically senses the eye in real-time using either photodiodes or camera and based on signal or image processing methods then estimates the motion of the eye to enable a compensation of the motion to be carried out at the diagnostic or surgery device to enable proper operation of this device and to avoid positioning errors.
Once an image of an eye has been taken it takes some time (processing time) until based on the image processing algorithm the position of the eye has been determined, this time is referred to as “latency”. If based on the eye position thus determined some feedback is to be given to a surgical or diagnostic device and if based on this feedback some position compensation should be carried out then the time necessary to carry out this compensation (e.g. by movement of the device or some of its parts) also contributes to the latency of the overall system.
One concrete example where such an eye tracking system is used in connection with a diagnostic or surgical device is a system for retinal video tracking for an Optical Coherence Tomography (OCT). An OCT system works similar to an ultrasound imaging device except that instead of ultrasound it uses infrared (IR) light which is emitted, reflected by the retina and then based on the reflected light and image processing methods a diagnostic image is obtained. Eye tracking with low latency effects can be implemented to ensure repeatable diagnostic images despite eye movements during image acquisition. The combined eyetracking OCT device then can be used for repeatably measuring thickness and structure of the retinal layers over time. Simarly, eye tracking with low latency effects is required for compensating eye movement during laser refractive surgery.
In such applications a measurement/correction device is operating at precise locations on the eye. In order to compensate the inherent eye-position changes, an eye-tracking system is usually employed. The eye-tracking system measures the eye-position at fixed intervals and communicates the data to the effectors system. The time elapsed between the measurement moment and the end of effectors system adjustment to the new position is defined as latency. The latency time includes the time required for performing the measurement, the communication time and the effectors (e.g. mirrors) adjustment time.
The latency time translates to an eye position uncertainty, called dynamic uncertainty, due to fact that eye movement in the elapsed time is unknown, and consequently it is desired to minimize the latency effects. It is therefore the object of the present invention to provide a method and an apparatus which reduces the latency effects of an eye tracking system.